This invention relates generally to digital-to-analog converters, and more particularly to fast, high resolution digital-to-analog converters applicable to digital words in fixed point, floating point, and logarithmic formats.
Digital-to-analog converters convert digital words into analog values, such as analog voltage values or analog current values. Digital words may be binary, ternary, etc., and may be expressed in any known format, such as a fixed-point, a floating point, or a logarithmic format. When the digital word is a fixed-point binary word having n bits (d), the corresponding analog value S may be generated by applying progressive power of two weightings to each bit.
An R-2R ladder network represents one conventional digital-to-analog converter that uses a network of resistor stages to apply the progressive weightings to each bit. Each stage of the network uses the same pair of resistors, where the resistance of one resistor is twice the resistance of the other resistor. By connecting n stages together, the R-2R ladder network applies reciprocal ratios 1:½:¼: . . . :2−(n−1) to the input bit values to convert an n-bit digital word into an analog value.
Accurate conversion from the digital domain to the analog domain using an R-2R ladder network requires highly accurate reciprocal ratios. Thus, R-2R ladder networks require high precision resistors, particularly for large digital words. Because it is difficult to maintain the requisite precision across a large number of resistors, R-2R ladder networks typically do not have sufficient accuracy for large digital words. While other conventional digital-to-analog converters may improve the accuracy, these digital-to-analog converters typically do so using highly complex and/or computationally slow circuitry. Therefore, there remains a need for fast, high resolution digital-to-analog converters.